Directive loop antenna



g- 15, 1950 H. A. WHEELER 2,518,736

DIRECTIVE LOOP ANTENNA Filed Aug. 27, 1946 I milk.

INVENTOR. HAROLD A.WHEELER Patented Aug. 15, 1950 Ha old A,1Whee r,.G N ck .Yt ass gn toflazeltjne Research. lnc flhicago. Ill., a corporationof Illinois A pli ation August 1-2 1946, Serial o 693 267 This. invention relates to tern. that. i directive the pane Qt its. con ucors. V

Lo p antennas. as h. are very well .iknewh in theartr. Qne. comm arraneehientce prise four coplanar radiating. csmduetors, e ch. abou h i length positioned to r lean-with pen c rners t the cond ctor ends a uhiiorrh .o om diteetieh l the plane of. th oop A sys e .ei th s type. havi g .i ur indep nden radi tors be, in envenient; o supp ehdhas u stant ally no direetivitmw erea certain ins al at ons the u e 9i di eetivelo p ant n a m y e, h ghly des rab e? I fl s an bject efi he presen invention, herere, ep evidela loop tenna ystem which avoids he a ement oned "l mi ati ns of .Pr or arrangements.

"It is another object of theinvention to provide a n 'improve lqop an enna sys m wh ch is directive in the-plane of the 10.0111. t

It is a'further object of-the invention; to provide anew and improyed loop-antenna system which has a simplified mechanical construction and directional inthe plane of the loop.

In accordance with the invention, a resonant directive loop antenna system comprises apair of similar} coplanar radiating conductors of V- shaped configuration. H The conductorsghave an effective diameter which is within the range from one 'te'nth "to one-fortieth of the operating Wave length, and'they are dis'posedin image relation Withreferenceto az-planeof symmetryrwith the ans-i1 a e a t c rical: l ngth with n :the ran from thr e eighths 1 9 hree-sixteenths of h operatin wa e length- The system includes means for connect n si nal-translati l pparatus to the-antenna at he otherpa r Q? the adiecen of. it eehdhetorswhere y he antenn system exhibits minimuni'mtlialiion his he direc- 8 Glaims. Cl. 25083.5j1)

valerts antenna. sys- '2 tion o the ppos te pa r o adjacen en of h onductors ,lhe enstnict ng l ehte ha sys em h diatihs conduc rs may const u e c o s of c nductiv ipes or, i de i e h may bej leng hs otfiat me al est p o ribb n includin one. or se eral. ra e nn t d nducte T se, alternati s a e equ v noia a t e adiation perti s of h te n ar concerned.- In co vert n o on t peoicon u tionto the other as for e am n. substi utin condu e ib ns p p sections, the ribbon width is selected to be, equal to twice the pipg diameter. In view. ofthe equiv aleneyref h se con uctor ement a the relation of their critical dimensions, the expression effeeti ediemet as u il i th s. s cification and the appended claims is intended to be generic and t .defi e a onductive p pe of .a recited diameter or a metallic ribbon having a width of. twice that diameter or other equivalents.

For a better understanding of the present invention, together with, other and further objects thereof, reference is bad to the followin descriptigntalsen in connection with the accompanying drawing, and'its scope will he pointed out in t e appen c aimslnjthedrawing, Fig. 1 represents a plan View of afloop antenna system embodying the invention;

Fig. 2 is anLelevational view of the arrangeme it ofFig. 1 Fig. 3 represents the directional characteristic of the 2 1 ntenna; while Fig. 41s a schematic representation of the antenna utilized in explaining its radiation properties.

Referring now more particularly to Fig. 1, the antenna system there represented is a directive 'horizontalloop. It is essentially diamond-shaped and comprises a pair of similar, coplanar radiating conductors of V-shaped configuration having an effective diameter d which is a substantial jractionof one-quarter of the operating wave length. The first conductor includes the sections or arms I!) and H while the other has arms [2 2,416.13. The'conductors 10, ll and I2, I3 are disposed in image relation with reference to a plane of symmetry so that the ends of one are spaced from the ends of the other, preferably by .a-s istaheewh h is com ara le wit the fie t diame er otthe wheat or IDV .3, nclusiv .Thesenaratien of ad ac nt condu tor ends i usually in the range from one-half to twice the effective diameter. The arms of each conductor, for the case under consideration, are circular in cross section, being constituted of sections of highly conductive pipe or tubing, and have an electrical length approximately equal to onequarter of the operating wave length, as indicated in Fig. 1. The arms H] and l l of the first conductor as well as the arms I2 and I3 of the other define an acute angle designated A while the remaining pair of angles of the loop, which occur at the open corners, are obtuse.

The horizontal loop antenna is equally useful for wave-signal transmission or reception. In either case, means are provided for connecting a wave-signal translating apparatus (not shown) with the antenna at only a single pair of the adjacent ends of conductors H], II and l2, l3. This means is illustrated in the drawing as an openwire transmission line TL connected with one pair of conductor ends, leaving the diagonally opposite pair of conductor ends open-circuited.

In the usual case, each of the conductor sections Ill-l3, inclusive, has an electrical length of one-quarter of the operating wave length, as indicated above, but this length may vary over a range from three-eighths to three-sixteenths of the operating wave length. The effective diameter d, which is said to be a substantial fraction of one-quarter of the operating wave length, is usually equal to one-twentieth of that wave length but may have any value within the range from one-tenth to one-fortieth. The acute angle A is one practical embodiment of the invention is equal to 45 degrees and is usually within a range of 30 to 60 degrees. However, it appears that the absolute limits of this angle are about 20 to 90 degrees.

The radiation characteristics of the antenna are represented by the curve of Fig. 3, which is a curve plotted on polar coordinates in terms of relative field strength. The antenna radiates horizontally polarized waves and is predominantly directive over a horizontal semi-circle facing the conductor ends to which the transmission line TL is connected. It exhibits minimum radiation in the direction of the other pair of conductor ends, as shown by the minor radiation extending in the opposite direction. Expressed differently, if the arrow F of Fig. 3 is considered to point to the forward direction of radiation, the backward radiation is substantially cancelled or attenuated. Consequently, the antenna has a substantial ratio of forward to backward radiation. This results from the physical aspects of the antenna as will be understood from the following discussion of the schematic representation of Fig. 4.

The open corners of the antenna represent points of current minimum and voltage maximum while current maximum and voltage minimum conditions are established at the closed corners, specifically, at the junctions of conductor sections l8, H and l2, [3. It is well known that a loop antenna composed of very thin conductors is highly resonant and therefore oscillates in substantially a pure standing wave but when thick conductors are employed, a traveling-wave ourrent component is introduced. Hence the anconductor section II. The extent of the phase change is determined by the conductor reactance and the radiation resistance. The reactance depends primarily on the thickness of the conductor sections while the radiation resistance is governed principally by the acute angle A defined by companion conductor sections. Thus, the antenna shape has two degrees of freedom which are selected, by utilizing physical dimensions of the order recited above, to effect approximate cancellation of radiation in the backward direction. i.

The selection of dimensions causes radiation from conductor section ID, for the instantaneous condition represented in Fig. 4, to produce a radiation component indicated by the vector V1. The slight leading phase of this radiation compensates for its longer path so that the vector V1 is of substantially the same phase but opposite polarity relative to the radiation component, indicated by the vector V2, from the companion conductor section H. Both vectors V1 and V2 represent back radiation, and since they are of opposite polarity they cancel one another. The leading phase-of the current in conductor section. I!) prevents cancellation in the forward direction of the components of radiation from the companion conductors l0 and II. Therefore, these radiating elements aid one another in that direction. The other pair of conductor sections I2 and 13 may be analyzed in similar fashion to show that backward radiation from the system is effectively cancelled while forward radiation is augmented in accordance with the radiation characteristics represented by the curve of Fig. 3.

An ideal horizontal loop antenna gives cancellation of radiation in the vertical direction but the use of relatively thick conductor sections prevents complete cancellation and produces a minor component of vertical radiation. Two horizontal loops of the type shown in Fig. 1 stacked vertically with a spacing of one-half the operating wave length eliminate the vertical radiation.

The use of thick conductor sections minimizes the reactance of the antenna system so that it is only moderately frequency-selective. This feature permits operation over a moderate band of frequencies with small variations of impedance.

The described antenna has a very simple construction and may be easily mounted in a desired location. The use of relatively thick conductors to achieve the desired directivity is also desirable from the standpoint of mechanical rigidity.

For convenience, the foregoing description relates principally to the use of the antenna for wave-signal transmission. As already indicated,

the functions of reception and transmission with any such antenna are unavoidably associated by the reciprocity theorem. Therefore, such terms as radiating conductor, "radiation characteristics and similar expressions are utilized in the text and appended claims in a generic sense to define an antenna structure in accordance with the invention Whether that antenna be used for signal transmission or reception.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modificationsmay be made therein without departin from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

sari-ease What is claimed'isz' 1.,A-resonant .directive'loop antenna System comprisingi a pair of Similar, coplanar radiat ing conductors of V-shaped configuration having an effective diameter substantially equal to one-twentieth of the operating wave length and disposed in imagerelationwith referenceito a plane of symmetry with the ends of "one spaced from the. ends of the'other; onexpairroi said adjacent ends of, said conductorsjhaving; a highly reflecting termination and thelarms :of each conductor individually having an electrical length substantially equal 'to one-quarter of said Wave length "and defining an acute angle; and-means f-or'con-necting signal-translating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna system exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

2. A resonant directive loop antenna system comprising: a pair of similar, coplanar radiating conductors of V-shaped (configuration and circular in cross section, having a diameter which is within the range from one-tenth to one-fortieth of the operating wave length and disposed in image relation with reference to a plane of symmetry with the ends of one spaced from the ends of the other; one pair of said adjacent ends of said conductors being open cir cuited and the arms of each conductor individually having an electrical length Within the range from threeeighths to three-sixteenths of said wave length and defining an acute angle; and means for connecting signal-translating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna system exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

3. A resonant directive loop antenna system comprising: a pair of similar, coplanar radiating conductors of V-shaped configuration having an efiective diameter within the range from one-tenth to one-fortieth of the operating wave length and disposed in image relation with reference to a plane of symmetry with the ends of one spaced from the ends of the other; one pair of said adjacent ends of said conductors having a highly reflecting termination and the arms of each conductor individually having an electrical length substantially equal to one-quarter of said wave length and defining an acute angle; and means for connecting signal-translating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna system exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

4. A resonant directive loop antenna system comprising: a pair of similar, coplanar radiating conductors of V-shaped configuration having an effective diameter which is within the range from one-tenth to one-fortieth of the operating wave length and disposed in image relation with reference to a plane of symmetry with the ends of one spaced from the ends of the other; one pair of said adjacent ends of said conductors having a highly reflecting termination and the arms of each conductor individually having an electrical length within the range from threeeighths to three-sixteenths of said wave length and defining an acute angle; and means for connecting signal-translating apparatus to said antenna at the other pair of said adjacent ends of said-conductors, whereby; said antenna system exhibits mini-mum :Vradiation inthe direction of the opposite-: pair of adjacent; ends of I said. conductors, J

5. A resonant directive loop antenna system comprising2a pairof similar, coplanar radiating conductors of V-shaped configuration having an effective diameter which is within the'range from one-tenth to one-fortieth of the operating wave lengthand disposed in image relation with reference to a plane of symmetry with the ends of one spaced. from the ends of the other; one pair of said adjacent ends of said conductors having amhighly reflecting termination, and the arms of each conductor individually having an electrical length within the range from threeeighths to three-sixteenths of said wave length and defining an angle of substantially forty-five degrees; and means for connecting signaltranslating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna system exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

6. A resonant directive loop antenna system comprising: a pair of similar, coplanar radiating conductors of v-shaped configuration having an efi'ective diameter which is within the range from one-tenth to one-fortieth 0f the operating Wave length and disposed in image relation with reference to a plane of symmetry with the ends of one spaced from the ends of the other; one pair of said adjacent ends of said conductors having a highly reflecting termination and the arms of each conductor individually having an electrical length within the range from threeeighths to three-sixteenths of said wave length and defining an angle within the range from Ethirty to sixty degrees; and means for connecting signal-translating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna systems exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

7. A resonant horizontal directive loop antenna system comprising: a pair of similar, coplanar horizontal radiating conductors of V- shaped configuration having an effective diameter which is within the range from one-tenth to one-fortieth of the operating wave length and disposed in image relation with reference to a plane of symmetry with the ends of one spaced from the ends of the other; one pair of said adjacent ends of said conductors having-a highly reflecting termination and the arms of each conductor individually having an electrical length within the range from three-eighths to threesixteenths of said wave length and defining an acute angle; and means for connecting signaltranslating apparatus to said antenna at the other pair Of said adjacent ends of said conductors, whereby said antenna system exhibits minimum horizontal radiation in the direction of the opposite pair of adjacent ends of said conductors.

8. A resonant directive loop antenna system comprising: a, pai of similar, coplanar radiating conductors of V-shaped configuration having an effective diameter which is within the range from one-tenth to one-fortieth of the operating wave length and disposed in image relation with reference to a plane of symmetry With the ends of one spaced from the ends of the other by a distance of the same order of magnitude as said eflective diameter; one pair of said adjacent ends of said conductors having a highly reflecting termination and the arms of each conductor individually having an electrical length within the range from three-eighths to threesixteenths of said wave length and defining an acute angle; and means for connecting signaltranslating apparatus to said antenna at the other pair of said adjacent ends of said conductors, whereby said antenna system exhibits minimum radiation in the direction of the opposite pair of adjacent ends of said conductors.

HAROLD A. WHEELER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS v Date Number Name 2,145,024 Bruce Jan. 24, 1939 2,207,781 Brown July 16, 1940 2,247,743 Beverage July 1, 1941 2,391,026 McGuigan Dec. 18, 1945 2,419,577 Libby Apr. 29', 19 7 FOREIGN PATENTS Number Country Date 462,459 Great Britain Mar. 4, 1937 

